! A unique feature of systemic sclerosis (SSc) is fibrosis in multiple organs that develops simultaneously. Lung and heart fibrosis currently account for most SSc-associated deaths, lack effective treatments and represent a major unmet need. Emergence of myofibroblasts from tissue-resident quiescent progenitors represents the unifying mechanism underlying all forms of fibrosis; however the factors that negatively regulate the process to promote fibrosis resolution remain unknown. Our recent multi-ethnic genetic study implicates the ubiquitin- editing enzyme A20 in fibrotic SSc phenotypes. A20 regulates NF-kB signaling and is linked with inflammatory diseases. However, despite its clinical relevance for SSc, the role of A20 in fibrosis has never been studied. Our preliminary results show that: 1) A20 expression is significantly reduced in skin and lungs from SSc patients, while the A20 suppressor DREAM is elevated; 2) A20 suppressed myofibroblast transition of multiple mesenchymal progenitor cell types by targeting several profibrotic pathways; and 3) DREAM expression is elevated in SSc and induced by TGF-, while DREAM suppresses A20. Based on these results, we propose the novel hypothesis that A20 has a distinct and previously-unrecognized vital role in restraining myofibroblast transition, and its compromised function in SSc contributes to increased fibrosis susceptibility in multiple organs. This paradigm shift from drivers to inhibitors of fibrosis as key targets has significant treatment implications. We will test our hypothesis in two distinct Specific Aims. Aim 1 will determine if mice with reduced A20 in all tissues, recapitulating compromised A20 in SSc, or with fibroblast-specific loss of A20, show increased fibrosis susceptibility in both inflammation-dependent and inflammation-independent models, and interrogate tissue-specific mechanisms relevant to human disease. To directly test if increasing tissue A20 limits fibrosis susceptibility, Aim 2 will measure fibrosis in mice lacking DREAM in all tissues or specifically in fibroblasts, and in mice treated with an FDA-approved anti-diabetic drug that de-represses A20 by blocking DREAM. Based on a sound premise strongly supported by emerging genetic, genomic and cellular data, this R21 will provide novel insight regarding A20 contribution and mechanisms in multi-organ fibrosis in SSc. Anticipated results will inform the development of innovative therapeutic strategies promoting fibrosis resolution. !